Prior art fiber-optic switchboards using light deflectors may be understood by reference to FIG. 1. In this figure, there is shown an array of input fibers and an array of output fibers. Each input fiber 10 has its own input lens 12 which collimates the light from its fiber. The collimated light from the input fibers falls on an array of deflector elements 14 backed by a mirror 16. There is one deflector element for each input fiber which deflects the light of its input fiber to any one of the output fibers 18. Each output fiber has its own output lens 20, whose function is to focus the collimated light into the associated output fiber. Thus any input fiber can have its light directed into any output fiber, and all fibers can be active at once.
The above configuration, however, is unsatisfactory for the following reasons:
1. The deflector must be very accurate and repeatable in order to get the beam into the output fiber. For example, if the output lens has a 10 mm focal length, and the acceptable deviation in position in the output spot is 25 .mu.m, then the required accuracy of the deflector must be within 0.15.degree..
2. The inhomogeneity in the deflector, which, for example, may be a conventional programmable or controllable light deflector on a diffraction grating of the type shown in U.S. Pat. No. 3,752,563 entitled Magnetic Film Stripe Domain Diffraction which issued in the name of Ernest J. Torok, David S. Lo and David I. Norman to the assignee of the present invention on Aug. 14, 1973, with variable grating spacing and orientation, must likewise be very small (0.15.degree. or 2.5 m rad).
3. The acceptance angle of the output fiber is greatly exceeded by the angle of incidence of the light from the array of input fibers. The further the input fibers are from each other, the larger the angle of incidence, and the greater the problem. Even if the input lenses were only 2 mm in diameter, a hexagonal array of 37 input lenses would have a maximum angle of incidence of 35.degree. which exceeds the acceptance angle of the output fiber by a factor of about 2.
The present invention furnishes a fast switching, compact, non-blocking fiber-optic switchboard with no moving parts which is capable of switching any input fiber to any output fiber when all inputs and outputs are simultaneously operating so that light from an input fiber may be deflected by a light deflecting element into any one of many output fibers .